The present invention relates to a catheter assembly insertable into a living body for biophysical (e.g. blood pressure or flow rate) or biochemical (e.g. blood pH or oxygen concentration) sensing at a region of interest. More particularly, the invention relates to compact configurations for such a catheter assembly adapting it for insertion through or into exceptionally small spaces, and for measuring multiple parameters simultaneously without sacrificing compactness.
Many prior art catheter assemblies, such as those shown in Mizuno et al., U.S. Pat. Nos. 4,274,423, DeRossi et al., 4,456,013, Adams et al., 4,683,757 and Ligtenberg et al., 4,722,348, employ solid-state electronic pressure transducers at their insertable ends. Such transducers have a pressure-sensing diaphragm, one side of which is exposed to the pressure to be measured and the other side of which communicates with a reference pressure passageway which extends into the catheter tube and is isolated from the pressure to be measured. To provide the reference pressure passageway, a special mounting structure for the pressure transducer must be included at the insertable end of the catheter assembly, increasing the transverse cross-sectional diameter of the insertable end and limiting the functions which it can perform within the available space.
Other types of transducers which are conventionally employed in catheter assemblies are those categorized generally as chemically sensitive semiconductor devices, or CHEMFETS. These solid-state electronic chemical transducers are capable of performing chemical analysis of blood and other fluids by ion detection, and measuring pH, gases, humidity, enzymes and other parameters. Despite the variety of available transducers, however, catheters usually employ only a single solid-state device at their insertable ends for measuring a single parameter, such as pressure. Such single-function devices require the sequential removal and insertion of multiple catheters having different transducers to obtain substantially contemporaneous readings of multiple parameters at a region of interest, but such multiple insertions increase the risk of injury to the patient as well as the time and expense of the procedure. Also, multiple insertions cannot simultaneously measure multiple parameters at an identical site to correlate exactly the relationship between the parameters. Although multi-function cathether assemblies having multiple transducers at their insertable ends have also been used in the past, such catheter assemblies have been limited with respect to their number of multiple functions primarily by space limitations affecting the maximum permissible transverse cross-sectional dimension of their insertable tips, dictated by the small areas of the blood vessels or other passageways into which the tips must be inserted.
Therefore, a need exists for catheter assemblies having an insertable tip of minimized transverse cross-section, yet capable of measuring pressure and simultaneously measuring multiple parameters.